It depends on many factors; how bad is the abuse, is it emotional or physical, how old are you, could you manage on your own or do you need their support, do you have/can you get a job etc etc
However, I would say that if they are hurting you (i.e, physical or sexual abuse) then you need to get out and get the police involved... but be careful how you define abuse - I knew a girl who got slapped by her mother for being a little bitch (which she was) and she got the police involved. The girl was not under threat (she was taller and stronger then her mother) and it only happened once and her mother was a lovely, and very reasonable woman. So the family wnt through a lot just because darling Steffi get the hump over a well earned slap.